Shade foe lamps



-KEMBLE BARTLETT,

Reflector.

Patented Oct. 20, 1857.

N. FEERS. Phuto-Lithogm vm. Waxhnglom D. c.

UNITED STATES i PATENT OFFICE.

WM. KEMBLE, OF NEW' YORK CITY, AND WM. H. C. BARTLETT, OF WEST POINT,NEW YORK.

SHADE FOR LAMPS. i

Specification of Letters Patent No..18,456, dated October 20, 1857'.

To' aZ'Z whom t may concem:

Be it known that we, VM. KEMBLE, of the city andSt-ate of New York, andVVILLIAM H. C. BARTLETT, of. West Point, county of Orange, and State ofNew York, have in vented certain new and useful Improvements inRefracting-Shades for Lamps, &c.; and we do hereby declare that thefollowing is a full, clear, and eXact description of the same, referencebeing made to the annexed drawing, making a part of this specification,that is to say: i

Our invention is for an improvement in the Construction of glass shadesfor lamps or other source of artificial light, and the object of oursaid improvement is to secure and concentrate n a horizontal directionall or as nearly all as is possible) those rays projected above or belowthe radiant point. In lighting cities and particularly in lighthousesthe rays sufl ered to escape vertically or nearly so are lost, theslight amount returned by refiection being too little to be taken intoaccount. In light houses this loss is avoided by the Fresnel system ofdetached rings or zones of prisms or by lenses. In our improved shadethe light is deflected also by zones of prismatic section, but theydiffer in Construction and arrangement, and they cliffer also by thegoverning principles by which they are arranged. In the Fresnel systemsome light is lost by refiection from the glass surfaces. This is adefect, and arises from the fact that the rays fall upon those surfacesat various angles, 'depending upon their position. But very few raysfall perpendicularly upon the interior surfaces,.

while in our improved shade all rays fall perpendicularly upon thereceiving surfaces of the material which is to refract them or causetheir deviation in the desired direction. Thus the rays of light sufl'erin passing the glass but one deviation, and that at the outer surface,which is a surface of accurate convergence and not spherical. As allrays fall upon the interior surfaces perpendicularly to those surfacesit :Eollows that whatever refiection takes place does so in thedirection of the radiant, and thus alls back upon the source of light.No loss can ocour therefore from this cause. A further advantageconsequent upon our improvement s the facility with which the instrumentcan be made and the comparatively slight cost of it. The

figure being one of revolution, eXternally and internally, the glass maybe ground and polished by turning, for the finest quality, or may bepressed in molds for the inferior ones; The eXternal surface of ourshade is perfectly smooth, and the shape is such that any sectionparallel to its equator would be a circle, while any sectionperpendicular to the equator would be ellipsoidal. The figurerepresented is such a section taken through the center. The interior isserrated by the formation of spherical' zones alternating with conicfrustums. The zones have their centers and the frustums their verticesat the center A, which is also the position for the light. From this itwill be seen that each ray proceeding from the light must fall per*pendicularly upon the zones (a) while none can fall upon the othersurfaces ('a') since' these are parallel with the direction of the rays,hence it follows that each ray will pass through the glass without beingrefracted until it emerges When all are deviated into the desireddirection. In the drawing these are shown as converging at B, but may bemade to issue in parallel rays or diverging ones according to the usesto which the light is to be put. As the surfaces of the zones arepolished, a portion of the light will necessarily be reflected, and hereit will be seen that a prominent feature of our invention lies in thedirection given to said refiected rays, Viz. by projecting them backupon the source of light, -whereby they are all saved and serve toincrease the intensity of the illumination. The proper shape of theexternal surface of the shade will be found by a calculation based uponthe index of refraction of the glass composing the same, and theintended direction of the rays. Thus the finding of the proper shape ofthe eX- ternal surface is reduced to a calculation of two elementsinstead of three, as would be the case were the inner surface of a shapeto refract the ray, and as is the case n the Fresnel system.

The shade may be made most conveniently of two parts, dividing it at theequator, and these may subsequently be cemented together. For certainpurposes the lower half may be omitted, or left as plain glass, and thisprobably will be the best form for street lights. When the ground is tobe illuminated the intercepted upward going rays instead of emergingparallel to the ground may be made to fall upon the ground at someproper distance, as for instance, at or near the next lamp post. Forlarge constructions, as

:for light houses, the envelop may be constructed in sections and builtup in the usual maner upon a suitable supporting frame.

To a. considerable eXtent the Construction of the shade With a singleinterior spherical Zone, that is, by producing in section the Circle ofthe smallest of the zones and making thereby a single Zone equal inWidth to the height of the shaide, Would produce the same results. Thedivergence of the rays Would be precisely the same, but light would belost by absorption in the larger amount of glass required, and hence thedivision of the interior surface by the conic frustums permits ofpresenting the greatest amount of receiving surface to the light and atthe same time of reducing the thickness of the glass to the least whichwill give the necessa'ry strength of Construction. This, then, is the'only purpose of the employment of those frustums, and it will besufiiciently obvious that were their Vertices at any point other thanthat of the radiant A some loss Would occur.

We claim The herein described method of constructing a refractinglight-shade that s to say* having its interior so shaped that all raysshell full perpendicularly upon the receiving surfaces in combinationWith un exterior refracting surface by which only the rays shell bedeviated into the required direction substantially as described herein.

WM. KEMBLE. W M. HIU. BARTLETT.

Wtnesses:

JOSEPH P. PIRSON, S. Hi MAYNARD.

